1. Field of the Invention
The present invention relates to a speed control apparatus for a cylinder, which makes it possible to automatically control the displacement speed of a piston by the aid of a speed controller for electrically controlling the flow rate of a pressure fluid introduced into and discharged from the cylinder.
2. Description of the Related Art
The pressure fluid-driven apparatus has been hitherto utilized extensively in order to drive and control the object by using a pressure fluid such as compressed air. FIG. 13 illustrates such a pressure fluid-driven apparatus as exemplified by a speed control circuit for controlling the operation speed of a cylinder.
The speed control circuit 1 comprises the cylinder 2, a selector valve 5 for making change over between a first port 4a and a second port 4b of the cylinder 2 for the pressure fluid supplied from a pressure fluid supply source 3, and a pair of speed controllers 6a, 6b installed to the pair of ports 4a, 4b of the cylinder 2 respectively.
In this case, the pressure fluid, which is supplied from the pressure fluid supply source 3, is supplied to the first or second port 4a (4b) of the cylinder 2 via the first or second speed controller 6a (6b) in accordance with the change over action of the selector valve 5. A piston 7, which is accommodated in a cylinder chamber of the cylinder 2, makes reciprocating motion at a predetermined speed in accordance with the action of the pressure fluid. Each of the speed controllers 6a, 6b generally comprises a variable throttle valve 8 and a check valve 9 which are combined in parallel in an integrated manner. The variable throttle valve 8 has an unillustrated valve stem formed with a knob (not shown) exposed to the outside. When an operator grips the knob to rotate the valve stem in a predetermined direction, the spacing distance (throttle amount) between the valve stem and a seat section is adjusted. As a result, the passage area at the inside of the valve is changed depending on the spacing distance between the valve stem and the seat section, and thus the flow rate of the pressure fluid, which is supplied to or discharged from the cylinder 2, is controlled.
However, the speed control circuit 1 for the cylinder 2 concerning the conventional technique involves the following drawback. That is, for example, every time when the operation speed of the cylinder 2 is changed due to any variation of the supply pressure of the pressure fluid supply source 3 or the like, the operator has to adjust the spacing distance (throttle amount) between the valve stem and the seat section by manually rotating the knob of each of the speed controllers 6a, 6b in the predetermined direction. The conventional speed control circuit 1 does not constructed such that the operation speed of the cylinder 2 is automatically controlled.
Further, for example, when the operation speed of the cylinder 2 is adjusted during the maintenance, the operator manually set or adjust the throttle amounts of a large number of speed controllers individually. Therefore, the conventional technique is complicated, and it involves such an inconvenience that the maintenance operation cannot be performed conveniently.